1. Field of the Invention
This invention relates to a flip-flop circuit which makes use of a resonant-tunneling effect.
2. Description of the Related Art
Various flip-flop circuits are conventionally known, and one of such conventional flip-flop circuits is disclosed, for example, in N. Yokoyama and K. Imamura, Electronics Lett., Vol. 22, p. 1228, 1986. The flip-flop circuit is shown in FIG. 6. Referring to FIG. 6, the flip-flop circuit shown includes a resonant-tunneling hot-electron transistor RHET.sub.0 grounded at the emitter electrode thereof. The base electrode of the resonant-tunneling hot-electron transistor RHET.sub.0 is connected to an input terminal Vin by way of an input resistor Rin.sub.0, and the collector electrode of the resonant-tunneling hot-electron transistor RHET.sub.0 is connected to a voltage source Vcc (whose power source potential is represented by Vcc.sub.0) by way of a load resistor R.sub.L0. Further, a junction between the load resistor R.sub.L0 and the collector terminal of the resonant-tunneling hot-electron transistor RHET.sub.0 is connected to an output terminal Vout. Here, the resonant-tunneling hot-electron transistor RHET.sub.0 is designed such that the base current IB.sub.0 has a negative differential resistance to the base-emitter voltage VBE.sub.0 but the collector current IC.sub.0 does not have a negative differential resistance to the base-emitter voltage VBE.sub.0. Since the base current IB.sub.0 has a negative differential resistance to the base-emitter voltage VBE.sub.0, if a bias potential Vin.sub.0 at the input terminal Vin is set suitably, then a bistable characteristic having a state (hereinafter referred to as state A.sub.0) wherein the base-emitter voltage VBE.sub.0 has a lower voltage and another state (hereinafter referred to as state B.sub.0) wherein the base-emitter voltage VBE.sub.0 has a higher voltage is obtained. Switching between the state A.sub.0 and the state B.sub.0 can be performed by applying a positive or negative voltage pulse to the input terminal Vin. Further, since the collector current IC.sub.0 does not have a negative differential resistance to the base-emitter voltage VBE.sub.0 and exhibits a monotone increase as the base-emitter voltage VBE.sub.0 increases, whether the current state is in the state A.sub.0 or in the state B.sub.0 can be read out from a potential Vout.sub.0 at the output terminal Vout, and a flip-flop operation is realized by this. The circuit described above is characterized in that a flip-flop operation can be realized with a comparatively small number of elements by making use of resonant-tunneling effect.
The conventional flip-flop circuit described above requires a resonance-tunneling hot-electron transistor (hereinafter referred to simply as RHET) whose base current has a negative differential resistance to the base-emitter voltage but whose collector current does not have a negative differential resistance to the base-emitter voltage. However, since a RHET has a resonant-tunneling barrier at an emitter-base interface, a negative differential resistance sometimes appears not only with the base current but also with the collector current depending upon the structures of the resonant-tunneling barrier and a collector barrier, and accordingly, it is not easy to obtain a desired element characteristic for realizing a flip-flop operation. In short, the conventional flip-flop circuit is complicated in element structure with the RHET and also in principle of operation and it is not easy to design the element. Further, where the temperature is approximately 300.degree. K. (10.degree. C. to 30.degree. C.), the RHET exhibits a decrease in current gain, and accordingly, there is another problem in that the conventional flip-flop does not operate well at a room temperature of 10.degree. C. to 30.degree. C.